Heretofore, space vehicles have been launched from space platforms into outer space and normally no attempt was made to recover the entire space vehicle for subsequent use after it has been returned to earth. One reason for this is that the space vehicle was normally damaged extensively by heat generated as it returned back through the atmosphere. In order to protect astronauts and space capsules forming part of the space vehicle from being injured or damaged by the re-entry heat, ablative coatings have been provided on the space capsule. Normally these ablative coatings were designed for a single re-entry trip. If it were desired to utilize the space capsule again, it would be necessary to remove the remains of the ablative coating from the space capsule and place another one thereon.
In recent developments in the space industry, it has been proposed to utilize a space vehicle which will be launched from earth and after orbiting the earth for a period of time, brought back to earth and landed on a runway. In order to protect the space vehicle from the extensive heat generated upon re-entering the earth's atmosphere, heat protective tiles have been placed on the skin of the space vehicle. The thickness of these tiles varies from approximately one inch up to approximately five inches depending on the particular surface that is to be protected and the exposure that that surface encounters during re-entry into the earth's atmosphere. These tiles are designed for absorbing the heat encountered in a large number of missions. It is anticipated that the space shuttle protected with these reusable tiles can be launched and recovered approximately one hundred times.
The shuttle reusable surface insulation (RSI) is composed of machined lightweight fused silica tiles, coated with a thin ceramic coating. This coating is very fragile and highly susceptible to damage, punctures, dings, chips and cracks. These damaged tiles must be removed and replaced if they cannot be repaired. To remove a tile from the skin of the space vehicle and to replace it with another undamaged tile is a time consuming and expensive procedure. Thus, it is desirable to provide a method of in situ repair of the tiles and it is estimated that 1/10th of the manpower is required to repair a tile in accordance with the present invention as compared to removing a tile and replacing it.
Repair of punctured or cracked thin glass has been relatively unsuccessful due to thermal stresses and has not been considered feasible. Attempts have been made to drill a hole at the base of the crack to prevent further crack propagation, but instances of puncture repair or crack healing are relatively non-existent. The process developed according to the invention is used to repair punctures, dings and chips in thin glass.
The RSI tiles that are to be repaired include a ceramic coating which is a borosilicate, reaction cured glass from 0.010 to 0.020" thick.